We report an observation of a stable solitonlike structure on the surface of a ferrofluid, generated by a local perturbation in the hysteretic regime of the Rosensweig instability. Unlike other pattern-forming systems with localized 2D structures, magnetic fluids are characterized by energy conservation; hence their mechanism of soliton stabilization is different from the previously discussed gain-loss balance mechanism. The radioscopic measurements of the soliton's surface profile suggest that locking on the wavelength defined by the nonmonotonic dispersion curve is instrumental in its stabilization.
The normal field instability in magnetic liquids is investigated experimentally by means of a radioscopic technique which allows a precise measurement of the surface topography. The dependence of the topography on the magnetic field is compared to results obtained by numerical simulations via the finite-element method. Quantitative agreement has been found for the critical field of the instability, the scaling of the pattern amplitude and the detailed shape of the magnetic spikes. The fundamental Fourier mode approximates the shape to within 10% accuracy for a range of up to 40% of the bifurcation parameter of this subcritical bifurcation. The measured control parameter dependence of the wavenumber differs qualitatively from analytical predictions obtained by minimization of the free energy.
A new experimental system showing a transition to spatiotemporal intermittency is presented. It consists of a ring of hundred oscillating ferrofluidic spikes. Four of five of the measured critical exponents of the system agree with those obtained from a theoretical model of directed percolation.
The drop pinch-off at a nozzle is studied experimentally for a glycerin-water mixture in surrounding air. The neck diameter of the fluid shrinks with constant velocity. After a distinct transition point, the shrink velocity switches to a smaller value. Before that transition point, the shape of the neck can well be described by a symmetric scaling function, as obtained from Stokes-flow theory of drop formation. This function gives way to an asymmetric scaling function in the final stage before pinch-off.
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